This paper deals with the psychiatrist Louis Le Guillant's (1900–1968) contribution to the development of labor psychology. He conducted research on industrial relations, service work, and clerical workers during the 1950s and the 1960s. His investigation of the service model was parallel to his interest to improve the medical staff and its role within the medical institution. He also considered the hospital not as a custodial function but as a medical service. This paper surveys his new interpretations of the pathological and his interpretation of mental disorders, partially influenced by the institutional psychiatric movement. It asserts that Le Guillant's involvement in labor psychology was part of a more global project: the shaping of a renewed public mental health service and a growing attention to people in everyday life.